WO2020002142A1 - Method for producing paraxylene using a simulated moving-bed step, and a step of fractionating two fractions in a two-section column - Google Patents

Method for producing paraxylene using a simulated moving-bed step, and a step of fractionating two fractions in a two-section column Download PDF

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Publication number
WO2020002142A1
WO2020002142A1 PCT/EP2019/066445 EP2019066445W WO2020002142A1 WO 2020002142 A1 WO2020002142 A1 WO 2020002142A1 EP 2019066445 W EP2019066445 W EP 2019066445W WO 2020002142 A1 WO2020002142 A1 WO 2020002142A1
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Prior art keywords
desorbent
fraction
fractions
ethylbenzene
xylenes
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PCT/EP2019/066445
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French (fr)
Inventor
Isabelle Prevost
Jérôme PIGOURIER
Gérard Hotier
Original Assignee
Axens
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Publication date
Application filed by Axens filed Critical Axens
Priority to JP2020572983A priority Critical patent/JP7361057B2/en
Priority to CN201980043987.6A priority patent/CN112585107B/en
Priority to KR1020207036182A priority patent/KR20210030273A/en
Priority to US17/256,290 priority patent/US11242302B2/en
Priority to EP19731299.4A priority patent/EP3814307B1/en
Publication of WO2020002142A1 publication Critical patent/WO2020002142A1/en

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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C7/00—Purification; Separation; Use of additives
    • C07C7/005—Processes comprising at least two steps in series
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D15/00—Separating processes involving the treatment of liquids with solid sorbents; Apparatus therefor
    • B01D15/08—Selective adsorption, e.g. chromatography
    • B01D15/10—Selective adsorption, e.g. chromatography characterised by constructional or operational features
    • B01D15/18—Selective adsorption, e.g. chromatography characterised by constructional or operational features relating to flow patterns
    • B01D15/1814—Selective adsorption, e.g. chromatography characterised by constructional or operational features relating to flow patterns recycling of the fraction to be distributed
    • B01D15/1821—Simulated moving beds
    • B01D15/1828—Simulated moving beds characterized by process features
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D15/00—Separating processes involving the treatment of liquids with solid sorbents; Apparatus therefor
    • B01D15/08—Selective adsorption, e.g. chromatography
    • B01D15/10—Selective adsorption, e.g. chromatography characterised by constructional or operational features
    • B01D15/18—Selective adsorption, e.g. chromatography characterised by constructional or operational features relating to flow patterns
    • B01D15/1814—Selective adsorption, e.g. chromatography characterised by constructional or operational features relating to flow patterns recycling of the fraction to be distributed
    • B01D15/1821—Simulated moving beds
    • B01D15/185—Simulated moving beds characterized by the components to be separated
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/14—Fractional distillation or use of a fractionation or rectification column
    • B01D3/143—Fractional distillation or use of a fractionation or rectification column by two or more of a fractionation, separation or rectification step
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/14—Fractional distillation or use of a fractionation or rectification column
    • B01D3/32—Other features of fractionating columns ; Constructional details of fractionating columns not provided for in groups B01D3/16 - B01D3/30
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C15/00—Cyclic hydrocarbons containing only six-membered aromatic rings as cyclic parts
    • C07C15/02—Monocyclic hydrocarbons
    • C07C15/067—C8H10 hydrocarbons
    • C07C15/08—Xylenes
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
    • C07C5/22—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by isomerisation
    • C07C5/27—Rearrangement of carbon atoms in the hydrocarbon skeleton
    • C07C5/2767—Changing the number of side-chains
    • C07C5/277—Catalytic processes
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C7/00—Purification; Separation; Use of additives
    • C07C7/04—Purification; Separation; Use of additives by distillation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C7/00—Purification; Separation; Use of additives
    • C07C7/12—Purification; Separation; Use of additives by adsorption, i.e. purification or separation of hydrocarbons with the aid of solids, e.g. with ion-exchangers
    • C07C7/13—Purification; Separation; Use of additives by adsorption, i.e. purification or separation of hydrocarbons with the aid of solids, e.g. with ion-exchangers by molecular-sieve technique
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Definitions

  • TECHNICAL FIELD Paraxylene is mainly used for the production of terephthalic acid and polyethylene terephthalate resins, to supply synthetic textiles, bottles, and more generally plastics.
  • the present invention relates to a process for obtaining high purity paraxylene using a specific sequence of steps making it possible to simplify the fractionation step.
  • the overhead stream from this column which contains the C8-aromatic isomers, is then sent to the paraxylene separation process which is generally a separation step by adsorption in a simulated moving bed.
  • the extract obtained at the end of the separation stage by adsorption in a simulated moving bed, which contains the paraxylene is then distilled by means of an extract column and then a toluene column, to obtain high paraxylene. purity.
  • Patent FR2862638 describes a process for producing paraxylene from a hydrocarbon feed, using two stages of separation in simulated moving bed, and two stages of isomerization. The disadvantage of this process is that it requires two stages of separation in a simulated moving bed which results in a significant increase in the cost of production.
  • Another advantage of the process according to the invention is that it can be used to advantage in revamping configurations of a xylene loop. Indeed, in this case the same raffinate column can be reused provided that it is supplied with the 2 raffinates introduced separately as described in step B according to the invention.
  • the abbreviation EB denotes ethylbenzene.
  • Metaxylene is designated by the abbreviation MX.
  • xylenes is understood to mean a mixture of at least two isomers chosen from orthoxylene, metaxylene, and paraxylene.
  • the abbreviation SMB is used to designate a simulated moving bed.
  • C9 + hydrocarbons is understood to mean hydrocarbons containing at least 9 carbon atoms.
  • C8 + hydrocarbons are understood to mean hydrocarbons containing at least 8 carbon atoms.
  • C8Aromatics also denoted C8A, denote aromatic hydrocarbons containing 8 carbon atoms chosen from EB, PX, OX, MX.
  • raffinate is intended to mean a mixture of C8A depleted in PX and which may contain desorbent, that is to say having a mass content of PX of less than 2.0%, preferably less than 1.5% and preferably 1.0%. .
  • the term “free” means a mass content of a given compound relative to the total mass of the fraction considered, for example in EB, of less than 0.5% by weight, preferably of less than 0.1% and preferably less than 0.01%.
  • residual quantity of a given compound is understood to mean an amount whose mass content relative to the total mass of the fraction considered is less than 5.0% by weight, preferably between 5.0 and 1.0, preferably between 4.0 and 1.0, and preferably between 3.0 and 1.0% by weight.
  • distillation column means 2 sections or 3 sections, a distillation column allowing the production of 2 or 3 fractions respectively.
  • FIG. 1a represents the general diagram of a Xylenes loop implementing a step of separation by adsorption, a step of fractionation, a step C of isomerization in the vapor phase.
  • FIG. 1b represents the stage B of distillation of the raffinate resulting from stage A according to the prior art.
  • FIG. 2 represents an implementation of the method according to the invention.
  • the present invention relates to a process for obtaining paraxylene from a feed containing xylenes, ethylbenzene and C9 + hydrocarbons, said process comprising
  • a single step A of separation in a simulated moving bed of said charge said step being carried out with a zeolite as adsorbent and a desorbent, at a temperature between 20 and 250 ° C., under a pressure comprised between the bubble pressure xylenes at operating temperature and 2.0 MPa, and with a volume ratio of the desorbent to the charge in the separation unit in simulated moving bed is between 0.4 and 2.5, and allowing obtaining at least three fractions,
  • stage B of fractionation by distillation in a distillation column of the fractions A21 and A22 resulting from stage A in which the said fractions are introduced separately at separate injection points and makes it possible to obtain a fraction B2 containing ethylbenzene, orthoxylene and metaxylene, and a fraction B42 free of aromatic compounds containing 8 carbon atoms and containing desorbent.
  • An advantage of the process according to the invention is to carry out a pre-fractionation during the step of separation into SMB which advantageously makes it possible to facilitate the step of fractionation of the raffinate without increasing the complexity of the process and without modifying the yield of Paraxylene.
  • Another advantage of the process according to the invention is that it can be used to advantage in revamping configurations of a xylene loop. Indeed, in this case the same raffinate column can be reused provided that it is supplied with the 2 raffinates introduced separately as described in step B according to the invention.
  • the method comprises a single step A of separation in a simulated moving bed implemented with a zeolite as adsorbent and a desorbent and making it possible to obtain at least three fractions, a fraction Al containing desorbent and paraxylene two fractions A21 and A22, also called "raffinate", depleted in paraxylene preferably comprising, in variable proportions, a mixture of EB, MX, OX, and the desorbent.
  • the proportions of EB, MX, OX and desorbent in the fractions A21 and A22 are different.
  • the fraction A21 has a mass content of desorbent lower than that of the fraction A22.
  • the separation step of said charge is implemented in a unit operating in a simulated moving bed in at least one separation column containing a plurality of interconnected beds and circulating desorbent in a closed loop from which the three fractions come:
  • the first is an Al extract comprising paraxylene and desorbent, so that after fractionation to remove the desorbent the PX reaches a commercial purity of minimum 99.0% and preferably 99.9% by weight.
  • the extract Al has at least 30% by weight of the total mass of the extract.
  • the depleted fraction A21 PX comprises, preferably consists, of a mixture of EB, MX, OX, and desorbent.
  • the adsorbent used in the separation unit in a simulated moving bed is a zeolite X exchanged with barium or a zeolite Y exchanged with potassium or a zeolite Y exchanged with barium and potassium.
  • the desorbent used in the separation unit in simulated moving bed is chosen from paradiethylbenzene, toluene, paradifluorobenzene or diethylbenzenes alone or as a mixture.
  • the volume ratio of the desorbent to the load in the simulated moving bed separation unit is between 0.4 and 2.5, preferably between 0.5 and 2.0 and preferably between 0, 5 and 1.5.
  • step A of separation in simulated moving bed is carried out at a temperature between 90 and 210 ° C, and more preferably between 160 and 200 ° C, and under a pressure between 1.0 and 2.2 MPa and preferably between 1.2 and 2.0 MPa.
  • the adsorber contains a plurality of beds, interconnected and distributed over several zones delimited by the injections of the filler and the desorbent, as well as withdrawals of the extract, and of the raffinates.
  • the total number of beds of the separation unit is between 10 and 30 beds, and preferably, between 15 and 18 beds distributed over one or more adsorbers, the number of beds being adjusted so that each bed has a height of between 0.70 and 1.40 m.
  • the distribution of the quantity of solid adsorbent in each zone of the separation unit (SMB) is as follows:
  • Each zone defines the injection and withdrawal points, fillers, desorbent, extract and raffinates as defined below:
  • o Zone 1 is between the injection of the desorbent B4 and the withdrawal of the extract Al.
  • o Zone 2 is between the withdrawal of the extract Al and the injection of the load o Zone 3A is between the injection of the load and the withdrawal of the raffmat A21 o Zone 3B, between the withdrawal of the raffinate A21 and withdrawal of raffmat A22 o Zone 4 is between the withdrawal of raffrnate A22 and the injection of desorbent B4
  • step A of adsorption of the C8A cut free of C9 + are characterized by:
  • the recovery rate of the PX in the extract Al defined by the ratio of PX in the extract Al / PX in the feed is at least equal to 97.0% and that after recovery of the desorbent, in the column of extract BC-l the minimum purity of the PX is 99.0% and preferably greater than 99.9%.
  • R (C8A) the quantities of C8A in the raffinate A21 / the quantity of C8A in the total raffinate A2 is at least 60% and preferably greater than 75%
  • R (Desorbent) the amount of desorbent in the raffinate A21 / the amount of desorbent in the total raffinate A2 the separation parameter "delta R" defined by the distribution difference R (C8A) - R (Desorbent).
  • the minimum separation parameter is 10%, preferably 20% and more preferably 30%.
  • the adsorption step A of the charge makes it possible to separate the PX, and also to prefragrate the raffinate A2 into two streams, one A21, enriched in C8A, and the other A22 enriched in desorbent.
  • Step B of fractionation The process according to the invention comprises a step B of fractionation by distillation in a column of the fractions A21 and A22 from step A of separation.
  • said fractions A21 and A22 are introduced separately into the raffinate column B-C2 at separate injection points.
  • step B makes it possible to produce at the top of the column a fraction B2 free of desorbent and depleted of PX and containing MX, OX and ethylbenzene and at the bottom a fraction B42 free of C8A and consisting of desorbent.
  • An advantage of this double feed is that it makes it possible to reduce the thermal load of the raffinate column by at least 2.0 to 15.0%, depending on the quality of the prefractionation of the raffinates obtained in step A.
  • step A is implemented so as to carry out a pre-fractionation into two raffmates A21 and A22, one enriched in desorbent, the other enriched in C8A (OX, MX, EB).
  • the desorbent used in step A is light, that is to say with a boiling point lower than that of C8A
  • the fraction of the raffinate whose light desorbent content is the highest is introduced a few trays above the position of the raffinate feed with the lowest content of light desorbent.
  • step B makes it possible to produce at the bottom of the column a fraction B2 free of desorbent and depleted in PX and containing MC, OC and ethylbenzene and at the top a fraction B42 free of C8A and consisting of desorbent.
  • the distillation column used is chosen from a 2-section column and a 3-section column.
  • said column has a number of theoretical plates of between 30 and 80, preferably between 35 and 75, preferably 40 and 70, very preferably between 45 and 65.
  • the two injection points of the fractions A21 and A22 in the distillation column have a spacing of between 2 and 15 theoretical plates, preferably between 3 and 12 theoretical plates and more preferably between 4 and 9.
  • the distillation column used is a 2-section column.
  • said 2-section column has a number of theoretical plates between 30 and 70, preferably between 35 and 65, preferably 40 and 60, very preferably between 45 and 55.
  • this spacing is correlated with the quality of the prefractionation of the raffinates carried out in step A.
  • the injection of fraction A22 will be done by a distribution system on different trays so that the spacing between the injection points of the charges A21 and A22 increases when the parameter separation R increases.
  • Said 2-section column further comprises a condenser and a reboiler, operated at 0.2 MPa with a reflux rate of 1.2.
  • the desorbent used in step A is a heavier compound than the xylenes, that is to say having a higher boiling point than that of the xylenes
  • the enriched raffinate by desorbing, ie the fraction A22 is introduced below the depleted raffinate by desorbing, ie the fraction A21.
  • the desorbent of said separation step is a lighter compound than the xylenes, that is to say having a lower boiling point than that of the xylenes
  • the raffinate enriched in desorbent that is to say the fraction A21
  • the desorbing that is to say the fraction A22.
  • the distillation column used is a 3-section column.
  • said column comprises an internal wall preferably placed in the rectification zone and makes it possible to collect two fractions B2 and B3 free of desorbent and a fraction B42 free of C8A and comprising, preferably consisting of desorbent.
  • the injection of the fractions A21 and A22 is carried out on either side of the internal wall.
  • the positions of the two supplies of the fractions A21 and A22 are located on either side of the internal wall.
  • the fraction Al originating from stage A containing, and preferably consisting of, a mixture of PX and desorbent is engaged in a fractionation stage by distillation in a distillation column (B-Cl) allowing the obtaining a fraction B1 free of desorbent consisting of PX and a fraction B41 consisting of desorbent.
  • Said distillation is carried out according to the knowledge of a person skilled in the art.
  • the desorbent fractions B41 and B42 free of C8A are recovered at the bottom of each distillation column, when the desorbent is heavy and at the head when the desorbent is light. Said fractions are then mixed and returned to step A of adsorption in a simulated moving bed by means of stream B4. Steam phase isomerization step C
  • the process further comprises a step C of isomerization in the vapor phase of the fraction B2 comprising ethylbenzene, orthoxylene and metaxylene from step B of fractionation.
  • step C of isomerization in the vapor phase allows the isomerization of the xylenes as well as of 1 ⁇ B, in a unit operating in the vapor phase, at high temperature and converting ethylbenzene into xylenes, to treat the raffinate B2 rich in EB from from step B.
  • the vapor phase isomerization stage makes it possible to convert 1 ⁇ B into xylenes with a pass conversion rate of ethylbenzene generally between 10 and 50%, preferably between 20 and 40%, with a loss of C8 Aromatics ( C8A) less than 5.0% by weight, preferably less than 3.0% by weight and preferably less than 1.8% by weight.
  • C8A C8 Aromatics
  • said step C also makes it possible to isomerize the xylenes, so that the paraxylene (PX) has a concentration at thermodynamic equilibrium; defined by
  • Ceff and Cin are the PX concentrations respectively in section C8A of the effluent and of the charge of the isomerization reactor,
  • Ceq is the thermodynamic equilibrium concentration of PX in section C8A at reaction temperature; greater than or equal to 90%.
  • the vapor phase isomerization step is carried out at a temperature above 300 ° C, preferably between 350 and 480 ° C, a pressure below 4.0 MPa, preferably between 0.5 and 2 0.0 MPa, a space velocity less than 10.0 h 1 , preferably between 0.5 and 6.0 h 1 , hydrogen to hydrocarbon molar ratio less than 10.0, preferably between 3.0 and 6, 0, and in the presence of a catalyst comprising at least one zeolite having channels whose opening is defined by a ring with 10 or 12 oxygen atoms (10 MR or 12 MR), and at least one metal from group VIII of content between 0.1 and 0.3% by weight.
  • a catalyst is used containing an acidic zeolite, for example of the structural type MFI, MOR, MAZ, FAU and / or EUO. Even more preferably, a catalyst is used containing a zeolite of structural type EUO and at least one metal from group VIII of the periodic table.
  • the catalyst used in step C comprises from 1 to 70% by weight of a zeolite of structural type Lt 10, preferably LU-1, comprising silicon and at least one element T preferably chosen among aluminum and boron whose Si / T ratio is between 5 and 100.
  • the zeolite is in hydrogen form at least in part, and the sodium content is such that the atomic ratio Na / T is lower at 0.1.
  • the catalyst comprises between 0.01 and 2% by weight of tin or indium, and sulfur in an amount of 0.5 to 2 atoms per atom of group VIII metal.
  • step C having concentrations of the PX, OX and MX isomer close to the thermodynamic equilibrium concentrations, are recycled to step A of adsorption in simulated mobile ht.
  • This example shows the advantage of the invention by comparing the performance of the distillation step B placed between an adsorption step A and an isomerization step C, said steps being part of an aromatic complex producing paraxylene at from a reformat.
  • this section C8A is sent in a step A of adsorption in a simulated moving bed comprising an adsorber with 4 zones delimited by the injections of charges and desorbent B4 and the withdrawals of Raffmat A2 and of extract Al.
  • This adsorber is composed of 15 beds containing X zeolite exchanged with barium distributed as follows:
  • the temperature is 175 ° C.
  • the desorbent used is Paradiethylbenzene, the level of solvent relative to the charge is 1.2 (vol / vol).
  • the adsorption separation unit A is used to produce 2 streams Al and A2 supplying the distillation step B:
  • said section C8A is sent in a step A of adsorption in a simulated moving bed comprising an adsorber with 5 zones delimited by the injections of fillers and desorbent ( B4) and the withdrawals of the raffmates A21, A22 and of extract Al.
  • Said adsorber is composed of 18 beds containing zeolite X exchanged with barium distributed as follows:
  • Zone 1 between the injection of the desorbent B4 and the withdrawal of the extract Al, o 6 beds in zone 2, between the withdrawal of the extract Al and the injection of the load, o 4 beds in zone 3A, between the injection of the load and the withdrawal of the A21 raffrnate, o 3 beds in zone 3B, between the withdrawal of raffinate A21 and the withdrawal of raffinate A22, o 2 beds in zone 4, between the withdrawal of raffinate A22 and the injection of desorbent B4.
  • the temperature is 175 ° C.
  • the desorbent used is Paradiethylbenzene, the level of solvent relative to the charge is 1.2 (vol / vol).
  • step A of the adsorption separation unit according to the invention makes it possible to obtain three fractions Al, A21, and A22, according to the following distribution.
  • the raffinates A21 and A22 are drawn off on either side of zone 3B of the unit A of adsorption in simulated moving bed, and have the following compositions:
  • step B of fractionation by the distillation column B-C2 containing 47 theoretical plates the raffinate A21 is fed to the theoretical plate 24, and the raffinate A22 is fed to the theoretical plate 30.
  • Said column further comprises a condenser and a reboiler, operated at 0.2 MPa with a reflux rate of 1.2. Said column makes it possible to produce the following 2 fractions:
  • Example 2 This example illustrates the advantage of the invention, when the performances of the prefractionation of the raffinate during the adsorption stage A vary, as can happen for example during a change of setting of the operating parameters of the adsorber or a change of molecular sieve.
  • the conditions of this example are identical to those of Example 1.
  • the position of the feed of the light raffinate A21 in the raffinate column is not impacted, that of the heavy raffinate is very slightly modified, the gain in thermal load of the reboiler increases significantly with the quality of the pre-fractionation of the raffinate.
  • the improvement of the adsorption capacities and selectivities of the molecular sieve can be used to reduce the energy consumption of the aromatic complex without modifying the configuration of the aromatic complex nor its performance in terms of productivity.

Abstract

The present invention describes a method for obtaining paraxylene from a feedstock containing xylenes, ethylbenzene and C9+ hydrocarbons, said method comprising: - a single simulated moving-bed separation step A implemented with a zeolite as adsorbent and a desorbent and allowing at least three fractions to be obtained, one fraction A1 comprising a mixture of paraxylene and desorbent, two fractions A21, A22 comprising ethylbenzene (EB), orthoxylene (OX) and metaxylene (MX) and desorbent, said step is carried out at a temperature of 20°C to 250°C, under a pressure between the bubble pressure of the xylenes at the operating temperature and 2.0 MPa, and with a volume ratio of the desorbent to the load in the simulated moving-bed separation unit 2 of 0.4 to 2.5; - a step B of fractionation by distillation in a two-section distillation column of fractions A21 and A22 from step A, in which said fractions are injected separately at separate injection points, allowing the production of a fraction B2 containing ethylbenzene, orthoxylene and metaxylene, and a fraction B42 free of aromatic compounds with eight carbon atoms and containing desorbent.

Description

PROCEDE DE PRODUCTION DE PARAXYLENE UTILISANT UNE ETAPE EN LIT MOBILE SIMULE, ET UNE ETAPE DE FRACTIONNEMENT DE DEUX FRACTIONS  PROCESS FOR PRODUCING PARAXYLENE USING A SIMULATED MOBILE BED STEP, AND A TWO-FRACTION FRACTIONATION STEP
DANS UNE COLONNES DE 2 COUPES.  IN A COLUMN OF 2 CUPS.
DOMAINE TECHNIQUE Le paraxylène est principalement utilisé pour les productions d’acide téréphtalique et de résines polyéthylène téréphtalate, pour fournir des textiles synthétiques, des bouteilles, et plus généralement des matières plastiques. TECHNICAL FIELD Paraxylene is mainly used for the production of terephthalic acid and polyethylene terephthalate resins, to supply synthetic textiles, bottles, and more generally plastics.
La présente invention concerne un procédé d’obtention de paraxylène à haute pureté mettant en œuvre un enchaînement spécifique d’étapes permettant de simplifier l’étape de fractionnement. ART ANTERIEUR The present invention relates to a process for obtaining high purity paraxylene using a specific sequence of steps making it possible to simplify the fractionation step. PRIOR ART
La production de paraxylène haute pureté mettant en œuvre une étape de séparation par adsorption est bien connue de l’art antérieur. De manière industrielle, ladite étape est réalisée au sein d’un enchaînement de procédés dit « boucle C8-aromatique » ou encore « boucle de xylène ». Cette « boucle C8-aromatique » inclut une étape d’élimination des composés lourds (c’est-à-dire contenant plus de 9 atomes de carbone, notés C9+) dans une colonne de distillation appelée « colonne des xylènes ». The production of high purity paraxylene using a separation step by adsorption is well known in the prior art. Industrially, said step is carried out within a chain of processes called "C8-aromatic loop" or even "xylene loop". This "C8-aromatic loop" includes a step of removing heavy compounds (that is to say containing more than 9 carbon atoms, denoted C9 +) in a distillation column called "xylenes column".
Le flux de tête de cette colonne, qui contient les isomères en C8-aromatiques, est ensuite envoyé dans le procédé de séparation du paraxylène qui est généralement une étape de séparation par adsorption en lit mobile simulé. L’extrait obtenu à l’issue de l’étape de séparation par adsorption en lit mobile simulé, qui contient le paraxylène est ensuite distillé au moyen d’une colonne d’extrait puis d’une colonne toluène, pour obtenir du paraxylène de haute pureté. The overhead stream from this column, which contains the C8-aromatic isomers, is then sent to the paraxylene separation process which is generally a separation step by adsorption in a simulated moving bed. The extract obtained at the end of the separation stage by adsorption in a simulated moving bed, which contains the paraxylene is then distilled by means of an extract column and then a toluene column, to obtain high paraxylene. purity.
Le raffinât obtenu à l’issu de l’étape de séparation par adsorption en lit mobile simulé, riche en métaxylène, orthoxylène et éthylbenzène, après une étape d’élimination du désorbant par distillation, le mélange est mis en œuvre dans une étape d’isomérisation, permettant l’obtention d’un mélange dans lequel la proportion des xylènes (ortho-, méta-, para- xylènes) est pratiquement à l’équilibre thermodynamique, et la quantité d’ éthylbenzène amoindrie. Ce mélange est à nouveau envoyé dans la « colonne des xylènes » avec la charge fraîche. L’art antérieur propose de nombreuses variantes de ce schéma de base mettant en œuvre une ou plusieurs étape de séparation (par adsorption, cristallisation, distillation ou par membrane) et/ou une ou plusieurs étape d’isomérisation en phase gazeuse (convertissant l’éthylbenzène par isomérisation en xylènes ou par désalkylation en benzène), ou en phase liquide (ne convertissant pas l’éthylbenzène). Le brevet FR2862638 décrit un procédé de production de paraxylène à partir d’une charge d’hydrocarbures, utilisant deux étapes de séparation en lit mobile simulé, et deux étapes d’isomérisation. L’inconvénient de ce procédé est de nécessiter deux étapes de séparation en lit mobile simulé qui entraîne une augmentation importante du coût de production. The raffinate obtained at the end of the separation step by adsorption in a simulated moving bed, rich in metaxylene, orthoxylene and ethylbenzene, after a step of removing the desorbent by distillation, the mixture is used in a step of isomerization, making it possible to obtain a mixture in which the proportion of xylenes (ortho-, meta-, para-xylenes) is practically at thermodynamic equilibrium, and the quantity of ethylbenzene is reduced. This mixture is again sent to the "xylenes column" with the fresh charge. The prior art proposes numerous variants of this basic scheme implementing one or more separation steps (by adsorption, crystallization, distillation or by membrane) and / or one or more isomerization steps in the gas phase (converting the ethylbenzene by isomerization to xylenes or by dealkylation to benzene), or in the liquid phase (not converting ethylbenzene). Patent FR2862638 describes a process for producing paraxylene from a hydrocarbon feed, using two stages of separation in simulated moving bed, and two stages of isomerization. The disadvantage of this process is that it requires two stages of separation in a simulated moving bed which results in a significant increase in the cost of production.
L’inconvénient principal de ces variantes est de complexifier le procédé en mettant en œuvre une ou plusieurs étapes d’adsorption ou d’isomérisation. Cette complexité augment de façon conséquente les coûts d’investissements pour la mise en œuvre desdits procédée. The main drawback of these variants is to complicate the process by implementing one or more adsorption or isomerization steps. This complexity significantly increases the investment costs for the implementation of said process.
Dans le domaine de l’invention, l’homme du métier cherche constamment à limiter la consommation énergétique du complexe aromatique en conservant la quantité de paraxylène à haute pureté obtenu. En effet l’impact énergétique revêt une importance grandissante pour les opérateurs compte tenu des incitations croissantes à réduire l’empreinte carbone de leur unités. In the field of the invention, a person skilled in the art constantly seeks to limit the energy consumption of the aromatic complex by conserving the quantity of high purity paraxylene obtained. Indeed, the energy impact is of increasing importance for operators given the increasing incentives to reduce the carbon footprint of their units.
De manière surprenante, la demanderesse a découvert que la combinaison dans un procédé d’obtention de paraxylène à haute pureté, d’une étape de séparation par adsorption en SMB produisant deux fractions contenant un mélange d’éthylbenzène (EB), métaxylène (MX),d’orthoxylène (OX), et de désorbant dans des proportions différentes, lesdites fractions étant engagées séparément dans une unique colonne de séparation par distillation permet avantageusement de faciliter l’étape de fractionnement du raffinât sans augmenter la complexité du procédé et sans modifier le rendement en Paraxylène. Surprisingly, the applicant has discovered that the combination in a process for obtaining high purity paraxylene, of a separation step by adsorption in SMB producing two fractions containing a mixture of ethylbenzene (EB), metaxylene (MX) , orthoxylene (OX), and desorbent in different proportions, said fractions being engaged separately in a single distillation separation column advantageously makes it possible to facilitate the fractionation step of the raffinate without increasing the complexity of the process and without modifying the Paraxylene yield.
Un autre avantage du procédé selon l’invention est de pouvoir être mise à profit dans des configurations de dégoulottage (« revamping ») d’une boucle xylènes. En effet, dans ce cas la même colonne de raffinât peut être réutiliser à condition de l’alimenter avec les 2 raffinats introduits séparément comme décrit dans l’étape B selon l’invention. Another advantage of the process according to the invention is that it can be used to advantage in revamping configurations of a xylene loop. Indeed, in this case the same raffinate column can be reused provided that it is supplied with the 2 raffinates introduced separately as described in step B according to the invention.
DEFINITIONS & ABREVIATIONS DEFINITIONS & ABBREVIATIONS
Dans l’ensemble de la description les termes ou abréviations ci-après ont le sens suivant. Il est précisé que, dans toute cette description, l’expression « compris(e) entre ... et ... » doit s’entendre comme incluant les bornes citées. Throughout the description, the terms or abbreviations below have the following meaning. It is specified that, throughout this description, the expression "comprised between ... and ..." must be understood as including the limits cited.
On désigne par l’abréviation EB, l’éthylbenzène. The abbreviation EB denotes ethylbenzene.
On désigne par l’abréviation PX, le paraxylène On désigne par l’abréviation OX, l’orthoxylène. It is designated by the abbreviation PX, paraxylene It is designated by the abbreviation OX, orthoxylene.
On désigne par l’abréviation MX, le métaxylène. Metaxylene is designated by the abbreviation MX.
On entend par xylènes (XYL), un mélange d’au moins deux isomères choisi parmi l’orthoxylène, le métaxylène, et le paraxylène. The term xylenes (XYL) is understood to mean a mixture of at least two isomers chosen from orthoxylene, metaxylene, and paraxylene.
On désigne par l’abréviation anglaise SMB, un lit mobile simulé. On entend par hydrocarbures en C9+, des hydrocarbures contenant au moins 9 atomes de carbone. The abbreviation SMB is used to designate a simulated moving bed. The term “C9 + hydrocarbons” is understood to mean hydrocarbons containing at least 9 carbon atoms.
On entend par hydrocarbures en C8+, des hydrocarbures contenant au moins 8 atomes de carbone. C8 + hydrocarbons are understood to mean hydrocarbons containing at least 8 carbon atoms.
On désigne par C8Aromatiques, encore noté C8A, les hydrocarbures aromatiques contenant 8 atomes de carbone choisi parmi le EB, le PX, le OX, le MX. C8Aromatics, also denoted C8A, denote aromatic hydrocarbons containing 8 carbon atoms chosen from EB, PX, OX, MX.
On entend par raffinât un mélange de C8A appauvri en PX et pouvant contenir du désorbant, c’est-à- dire présentant une teneur massique en PX inférieur à 2,0%, de préférence inférieur à 1,5% et de manière préférée à 1,0%. . The term “raffinate” is intended to mean a mixture of C8A depleted in PX and which may contain desorbent, that is to say having a mass content of PX of less than 2.0%, preferably less than 1.5% and preferably 1.0%. .
On entend par exempt au sens de la présente invention, une teneur massique en un composé donné par rapport à la masse total de la fraction considérée, par exemple en EB, inférieure à 0,5% poids, de préférence inférieur à 0,1% et de manière préférée inférieure à 0,01%. On entend par quantité résiduelle d’un composé donné, une quantité dont la teneur massique par rapport à la masse total de la fraction considérée est inférieure à 5,0% poids, de préférence comprise entre 5,0 et 1,0, de préférence comprise entre 4,0 et 1,0, et de manière préférée entre 3,0 et 1,0% poids. For the purposes of the present invention, the term “free” means a mass content of a given compound relative to the total mass of the fraction considered, for example in EB, of less than 0.5% by weight, preferably of less than 0.1% and preferably less than 0.01%. The term “residual quantity of a given compound” is understood to mean an amount whose mass content relative to the total mass of the fraction considered is less than 5.0% by weight, preferably between 5.0 and 1.0, preferably between 4.0 and 1.0, and preferably between 3.0 and 1.0% by weight.
Dans la présente invention, les termes raffinats, effluents, flux et fractions sont employés de façon équivalentes. On entend par colonne de distillation 2 coupes ou 3 coupes, une colonne de distillation permettant l’obtention de 2 ou 3 fractions respectivement. PRESENTATION SUCCINCTE DES FIGURES In the present invention, the terms raffinates, effluents, flows and fractions are used in an equivalent manner. The term “distillation column” means 2 sections or 3 sections, a distillation column allowing the production of 2 or 3 fractions respectively. SHORT PRESENTATION OF THE FIGURES
La figure la représente le schéma général d’une boucle Xylènes mettant en œuvre une étape de séparation par adsorption, une étape de fractionnement, une étape C d’isomérisation en phase vapeur. FIG. 1a represents the general diagram of a Xylenes loop implementing a step of separation by adsorption, a step of fractionation, a step C of isomerization in the vapor phase.
La figure lb représente l’étape B de distillation du raffinât issu de l’étape A selon l’art antérieur. La figure 2 représente une mise en œuvre du procédé selon l’invention . FIG. 1b represents the stage B of distillation of the raffinate resulting from stage A according to the prior art. FIG. 2 represents an implementation of the method according to the invention.
DESCRIPTION DETAILLEE DE L’INVENTION DETAILED DESCRIPTION OF THE INVENTION
Les caractéristiques et avantages du procédé selon l’invention, apparaîtront à la lecture de la description ci-après d’exemples non limitatifs de réalisations, en se référant aux figures annexées et décrites ci- après. Dans le sens de la présente invention, les différents modes de réalisation présentés peuvent être utilisés seuls ou en combinaison les uns avec les autres, sans limitation de combinaison. The characteristics and advantages of the method according to the invention will appear on reading the description below of nonlimiting examples of embodiments, with reference to the appended figures and described below. In the sense of the present invention, the various embodiments presented can be used alone or in combination with each other, without limitation of combination.
La présente invention concerne un procédé d’obtention de paraxylène à partir d’une charge contenant des xylènes, de l’éthylbenzène et des hydrocarbures en C9+, ledit procédé comprenant The present invention relates to a process for obtaining paraxylene from a feed containing xylenes, ethylbenzene and C9 + hydrocarbons, said process comprising
- une unique étape A de séparation en lit mobile simulé de ladite charge, ladite étape étant mise en œuvre avec une zéolithe comme adsorbant et un désorbant, à une température comprise entre 20 et 250°C, sous une pression comprise entre la pression de bulle des xylènes à la température opératoire et 2,0 MPa, et avec un rapport volumique du désorbant sur la charge dans l’unité de séparation en lit mobile simulé est compris entre 0,4 et 2,5, et permettant l’obtention d’au moins trois fractions,  a single step A of separation in a simulated moving bed of said charge, said step being carried out with a zeolite as adsorbent and a desorbent, at a temperature between 20 and 250 ° C., under a pressure comprised between the bubble pressure xylenes at operating temperature and 2.0 MPa, and with a volume ratio of the desorbent to the charge in the separation unit in simulated moving bed is between 0.4 and 2.5, and allowing obtaining at least three fractions,
■ une fraction Al comprenant un mélange de paraxylène et de désorbant, et ■ an Al fraction comprising a mixture of paraxylene and desorbent, and
■ deux fractions A21, A22 comprenant de l’éthylbenzène (EB), de l’orthoxylène (OX) et du métaxylène (MX) et du désorbant, ■ two fractions A21, A22 comprising ethylbenzene (EB), orthoxylene (OX), and metaxylene (MX) and desorbent,
- une étape B de fractionnement par distillation dans une colonne de distillation des fractions A21 et A22 issue de l’étape A, dans laquelle lesdites fractions sont introduites séparément à des points d’injections distincts et permet l’obtention d’une fraction B2 contenant de l’éthylbenzène, de l’orthoxylène et du métaxylène, et une fraction B42 exempte de composés aromatique contenant 8 atomes de carbones et contenant du désorbant. Un avantage du procédé selon l’invention est de réaliser un préfractionnement lors de l’étape de séparation en SMB ce qui permet avantageusement de faciliter l’étape de fractionnement du raffinât sans augmenter la complexité du procédé et sans modifier le rendement en Paraxylène. a stage B of fractionation by distillation in a distillation column of the fractions A21 and A22 resulting from stage A, in which the said fractions are introduced separately at separate injection points and makes it possible to obtain a fraction B2 containing ethylbenzene, orthoxylene and metaxylene, and a fraction B42 free of aromatic compounds containing 8 carbon atoms and containing desorbent. An advantage of the process according to the invention is to carry out a pre-fractionation during the step of separation into SMB which advantageously makes it possible to facilitate the step of fractionation of the raffinate without increasing the complexity of the process and without modifying the yield of Paraxylene.
Un autre avantage du procédé selon l’invention est de pouvoir être mise à profit dans des configurations de dégoulottage (« revamping ») d’une boucle xylènes. En effet, dans ce cas la même colonne de raffinât peut être réutiliser à condition de l’alimenter avec les 2 raffinats introduits séparément comme décrit dans l’étape B selon l’invention. Another advantage of the process according to the invention is that it can be used to advantage in revamping configurations of a xylene loop. Indeed, in this case the same raffinate column can be reused provided that it is supplied with the 2 raffinates introduced separately as described in step B according to the invention.
Etape A de séparation en lit mobile simulé Step A of separation in simulated moving bed
Selon l’invention, le procédé (figure 2) comprend une unique étape A de séparation en lit mobile simulé mise en œuvre avec une zéolithe comme adsorbant et un désorbant et permettant l’obtention au moins trois fractions, une fraction Al contenant du désorbant et du paraxylène deux fractions A21 et A22, encore appelé « raffinât », appauvri en paraxylène comprenant de préférence constituées, dans des proportions variables d’un mélange de EB, MX, OX, et du désorbant. According to the invention, the method (FIG. 2) comprises a single step A of separation in a simulated moving bed implemented with a zeolite as adsorbent and a desorbent and making it possible to obtain at least three fractions, a fraction Al containing desorbent and paraxylene two fractions A21 and A22, also called "raffinate", depleted in paraxylene preferably comprising, in variable proportions, a mixture of EB, MX, OX, and the desorbent.
Avantageusement, les proportions en EB, MX, OX et désorbant dans les fractions A21 etA22 sont différentes. De préférence, la fraction A21 présente une teneur massique en désorbant inférieure à celle de la fraction A22. Advantageously, the proportions of EB, MX, OX and desorbent in the fractions A21 and A22 are different. Preferably, the fraction A21 has a mass content of desorbent lower than that of the fraction A22.
L’étape de séparation de ladite charge est mise en œuvre dans une unité opérant en lit mobile simulé dans au moins une colonne de séparation contenant une pluralité de lits interconnectés et faisant circuler du désorbant en boucle fermée dont sont issus les trois fractions : The separation step of said charge is implemented in a unit operating in a simulated moving bed in at least one separation column containing a plurality of interconnected beds and circulating desorbent in a closed loop from which the three fractions come:
• la première est un extrait Al comprenant du paraxylène et du désorbant, de telles sorte qu’ après fractionnement pour éliminer le désorbant le PX atteigne une pureté commerciale de minimum 99,0 % et préférentiellement 99,9 % poids. Avantageusement, l’extrait Al présente au moins 30% poids de la masse total de l’extrait.  • the first is an Al extract comprising paraxylene and desorbent, so that after fractionation to remove the desorbent the PX reaches a commercial purity of minimum 99.0% and preferably 99.9% by weight. Advantageously, the extract Al has at least 30% by weight of the total mass of the extract.
• la fraction A21 appauvrie PX comprend, de préférence est constituée, d’un mélange de EB, de MX, OX, et de désorbant.  • the depleted fraction A21 PX comprises, preferably consists, of a mixture of EB, MX, OX, and desorbent.
• la fraction A22 appauvrie en PX et une quantité résiduelle d’EB et contient un mélange MX, OX, et du désorbant.  • the fraction A22 depleted in PX and a residual amount of EB and contains a mixture of MX, OX, and desorbent.
De préférence, l’adsorbant utilisé dans l’unité de séparation en lit mobile simulé est une zéolithe X échangée au baryum ou une zéolithe Y échangée au potassium ou une zéolithe Y échangée au baryum et au potassium. De préférence, le désorbant utilisé dans l’unité de séparation en lit mobile simulé est choisi parmi le paradiéthylbenzène, le toluène, le paradifluorobenzène ou des diéthylbenzènes seul ou en mélange. Preferably, the adsorbent used in the separation unit in a simulated moving bed is a zeolite X exchanged with barium or a zeolite Y exchanged with potassium or a zeolite Y exchanged with barium and potassium. Preferably, the desorbent used in the separation unit in simulated moving bed is chosen from paradiethylbenzene, toluene, paradifluorobenzene or diethylbenzenes alone or as a mixture.
De préférence, le rapport volumique du désorbant sur la charge dans l’unité de séparation en lit mobile simulé est compris entre 0,4 et 2,5, de préférence compris entre 0,5 et 2,0 et de manière préférée entre 0,5 et 1,5. Preferably, the volume ratio of the desorbent to the load in the simulated moving bed separation unit is between 0.4 and 2.5, preferably between 0.5 and 2.0 and preferably between 0, 5 and 1.5.
De préférence, l’étape A de séparation en lit mobile simulé est mise en œuvre à une température comprise entre 90 et 2lO°C, et de manière encore préférée entre 160 et 200°C, et sous une pression comprise entre 1 ,0 et 2,2 MPa et de préférence comprise entre 1 ,2 et 2,0 MPa. Preferably, step A of separation in simulated moving bed is carried out at a temperature between 90 and 210 ° C, and more preferably between 160 and 200 ° C, and under a pressure between 1.0 and 2.2 MPa and preferably between 1.2 and 2.0 MPa.
De préférence, l’adsorbeur contient une pluralité de lits, interconnectés et répartis sur plusieurs zones délimitées par les injections de la charge et du désorbant , ainsi que des soutirages de l’extrait, et des raffinats. Preferably, the adsorber contains a plurality of beds, interconnected and distributed over several zones delimited by the injections of the filler and the desorbent, as well as withdrawals of the extract, and of the raffinates.
Selon un mode particulier de réalisation, le nombre total de lits de l’unité de séparation (SMB) est compris entre 10 et 30 lits, et de manière préférée, entre 15 et 18 lits répartis sur un ou plusieurs adsorbeurs, le nombre de lits étant ajusté de manière à ce que chaque lit ait de une hauteur comprise entre 0,70 et 1,40 m. According to a particular embodiment, the total number of beds of the separation unit (SMB) is between 10 and 30 beds, and preferably, between 15 and 18 beds distributed over one or more adsorbers, the number of beds being adjusted so that each bed has a height of between 0.70 and 1.40 m.
Selon un mode particulier de réalisation, la répartition de la quantité de solide adsorbant dans chaque zone de l’unité de séparation (SMB) est la suivante : According to a particular embodiment, the distribution of the quantity of solid adsorbent in each zone of the separation unit (SMB) is as follows:
• la quantité de solide adsorbant en zone 1 est de l8%±8%,  • the amount of solid adsorbent in zone 1 is 18% ± 8%,
• la quantité de solide adsorbant en zone 2 est de 4l%±8%,  • the quantity of solid adsorbent in zone 2 is 41% ± 8%,
• la quantité de solide adsorbant en zone 3 A est de l8%±8%,  • the amount of solid adsorbent in zone 3 A is 18% ± 8%,
• la quantité de solide adsorbant en zone 3B est de l4%±8%.  • the amount of solid adsorbent in zone 3B is 14% ± 8%.
• la quantité de solide adsorbant en zone 4 est de 9%±8%.  • the quantity of solid adsorbent in zone 4 is 9% ± 8%.
Chaque zone délimite les points d’injection et de soutirage, des charge, désorbant, extrait et raffinats comme défini ci-dessous : Each zone defines the injection and withdrawal points, fillers, desorbent, extract and raffinates as defined below:
o La Zone 1 est comprise entre l’injection du désorbant B4 et le soutirage de l’extrait Al.  o Zone 1 is between the injection of the desorbent B4 and the withdrawal of the extract Al.
o La zone 2 est comprise entre le soutirage de l’extrait Al et l’injection de la charge o La zone 3A est comprise entre l’injection de la charge et le soutirage du raffmat A21 o La zone 3B, comprise entre le soutirage du raffinât A21 et le soutirage du raffmat A22 o La zone 4 est comprise entre le soutirage du raffrnat A22 et l’injection du désorbant B4 o Zone 2 is between the withdrawal of the extract Al and the injection of the load o Zone 3A is between the injection of the load and the withdrawal of the raffmat A21 o Zone 3B, between the withdrawal of the raffinate A21 and withdrawal of raffmat A22 o Zone 4 is between the withdrawal of raffrnate A22 and the injection of desorbent B4
Avantageusement, les performances de l’étape A d’adsorption de la coupe C8A exempte de C9+ sont caractérisées par : Advantageously, the performances of step A of adsorption of the C8A cut free of C9 + are characterized by:
- le taux de récupération du PX dans l’extrait Al définit par le ratio de PX dans l’extrait Al / PX dans la charge soit au moins égal à 97,0% et que après récupération du désorbant, dans la colonne d’extrait BC-l la pureté minimum du PX soit de 99,0% et préférentiellement supérieure à 99,9 %.  the recovery rate of the PX in the extract Al defined by the ratio of PX in the extract Al / PX in the feed is at least equal to 97.0% and that after recovery of the desorbent, in the column of extract BC-l the minimum purity of the PX is 99.0% and preferably greater than 99.9%.
La répartition des C8A entre les deux raffmats A21, A22 définie par : The distribution of C8A between the two raffmates A21, A22 defined by:
R(C8A) = les quantités de C8A dans le raffinât A21 / la quantité de C8A dans le raffinât total A2 soit au minimum de 60% et préférentiellement supérieure à 75%  R (C8A) = the quantities of C8A in the raffinate A21 / the quantity of C8A in the total raffinate A2 is at least 60% and preferably greater than 75%
La répartition du désorbant entre les deux raffinats A21, A22 définie par : The distribution of the desorbent between the two raffinates A21, A22 defined by:
R(Désorbant) = la quantité de désorbant dans le raffinât A21/ la quantité de désorbant dans le raffinât total A2 le paramètre de séparation « delta R » définit par l’écart de répartition R(C8A)- R(Désorbant) . De préférence, le paramètre de séparation minimum est de 10%, préférentiellement de 20% et plus préférentiellement de 30%.  R (Desorbent) = the amount of desorbent in the raffinate A21 / the amount of desorbent in the total raffinate A2 the separation parameter "delta R" defined by the distribution difference R (C8A) - R (Desorbent). Preferably, the minimum separation parameter is 10%, preferably 20% and more preferably 30%.
Ainsi l’étape d’adsorption A de la charge permet de séparer le PX, et également de préfractionner le raffinât A2 en deux flux l’un A21, enrichi en C8A, et l’autre A22 enrichi en désorbant. Thus, the adsorption step A of the charge makes it possible to separate the PX, and also to prefragrate the raffinate A2 into two streams, one A21, enriched in C8A, and the other A22 enriched in desorbent.
Etape B de fractionnement Le procédé selon l’invention comprend une étape B de fractionnement par distillation dans une colonne des fractions A21 et A22 issues de l’étape A de séparation. Step B of fractionation The process according to the invention comprises a step B of fractionation by distillation in a column of the fractions A21 and A22 from step A of separation.
Selon l’invention, lesdites fractions A21 et A22 sont introduites séparément dans la colonne de raffinât B-C2 à des points d’injections distincts. According to the invention, said fractions A21 and A22 are introduced separately into the raffinate column B-C2 at separate injection points.
Dans un mode particulier de l’invention où le désorbant utilisé dans l’étape A est lourd, c’est-à-dire avec un point d’ébullition supérieur à celui des C8A, la fraction dont la teneur en désorbant lourd est la plus élevée est introduite quelques plateaux en dessous de la position de l’alimentation de la fraction dont la teneur en désorbant lourd est la plus faible. Avantageusement, l’étape B permet de produire en tête de colonne une fraction B2 exempte de désorbant et appauvrie de PX et contenant le MX, OX et l’éthylbenzène et en fond une fraction B42 exempte de C8A et constitué de désorbant. In a particular embodiment of the invention where the desorbent used in step A is heavy, that is to say with a boiling point higher than that of C8A, the fraction with the highest content of heavy desorbent a few trays are introduced below the feed position of the fraction with the lowest content of heavy desorbent. Advantageously, step B makes it possible to produce at the top of the column a fraction B2 free of desorbent and depleted of PX and containing MX, OX and ethylbenzene and at the bottom a fraction B42 free of C8A and consisting of desorbent.
Un avantage de cette double alimentation est de permettre de réduire la charge thermique de la colonne de raffinât d’au minimum de 2,0 à 15,0 %, selon la qualité du préfractionnement des raffinats obtenue à l’étape A. An advantage of this double feed is that it makes it possible to reduce the thermal load of the raffinate column by at least 2.0 to 15.0%, depending on the quality of the prefractionation of the raffinates obtained in step A.
Cette avantage peut être obtenu pour tout type de désorbant dans la mesure où ladite étape A est mise en œuvre de telle sorte à effectuer un préfractionnement en deux raffmats A21 et A22 l’un enrichi en désorbant, l’autre enrichi en C8A (OX, MX, EB). Dans un mode particulier de l’invention où le désorbant utilisé dans l’étape A est léger, c’est-à-dire avec un point d’ébullition inférieur à celui des C8A, la fraction du raffinât dont la teneur en désorbant léger est la plus élevée est introduite quelques plateaux au-dessus de la position de l’alimentation du raffinât dont la teneur en désorbant léger est la plus faible. This advantage can be obtained for any type of desorbent insofar as said step A is implemented so as to carry out a pre-fractionation into two raffmates A21 and A22, one enriched in desorbent, the other enriched in C8A (OX, MX, EB). In a particular embodiment of the invention where the desorbent used in step A is light, that is to say with a boiling point lower than that of C8A, the fraction of the raffinate whose light desorbent content is the highest is introduced a few trays above the position of the raffinate feed with the lowest content of light desorbent.
Avantageusement, l’étape B permet de produire en fond de colonne une fraction B2 exempte de désorbant et appauvrie en PX et contenant le MC,OC et l’éthylbenzène et en tête une fractionB42 exempte de C8A et constitué de désorbant. Advantageously, step B makes it possible to produce at the bottom of the column a fraction B2 free of desorbent and depleted in PX and containing MC, OC and ethylbenzene and at the top a fraction B42 free of C8A and consisting of desorbent.
De préférence, la colonne de distillation mise en œuvre est choisi parmi une colonne 2 coupes et une colonne 3 coupes. Preferably, the distillation column used is chosen from a 2-section column and a 3-section column.
Avantageusement, ladite colonne présente un nombre de plateaux théoriques compris entre 30 et 80, de préférence entre 35 et 75, de manière préférée 40 et 70, de manière très préférée entre 45 et 65. Advantageously, said column has a number of theoretical plates of between 30 and 80, preferably between 35 and 75, preferably 40 and 70, very preferably between 45 and 65.
De préférence, les deux points d’injections des fractions A21 et A22 dans la colonne de distillation présente un écartement compris entre 2 et 15 plateaux théoriques, de préférence entre 3 et 12 plateaux théoriques et plus préférentiellement entre 4 et 9. Preferably, the two injection points of the fractions A21 and A22 in the distillation column have a spacing of between 2 and 15 theoretical plates, preferably between 3 and 12 theoretical plates and more preferably between 4 and 9.
Dans un mode de réalisation préféré, la colonne de distillation mise en œuvre est une colonne 2 coupes. In a preferred embodiment, the distillation column used is a 2-section column.
Avantageusement, ladite colonne 2 coupes présente un nombre de plateaux théoriques compris entre 30 et 70, de préférence entre 35 et 65, de manière préférée 40 et 60, de manière très préférée entre 45 et 55. Sans être lié à aucune théorie, il a été découvert que, pour minimiser la charge thermique de la colonne de raffinât cet écartement est corrélé à qualité du préfractionnement des raffinats opéré dans l’étape A. De préférence afin de minimiser la charge thermique de la colonne B-C2 lorsque la qualité du préfractionnement varie, l’injection de la fraction A22 se fera par un système de distribution sur différents plateaux de telle sorte que l’écartement entre les points d’injection des charges A21 et A22 augmente lorsque le paramètre de séparation R augmente. Ladite colonne 2 coupes comprend en outre un condenseur et un rebouilleur, opérée à 0,2 MPa avec un taux de reflux de 1 ,2. Advantageously, said 2-section column has a number of theoretical plates between 30 and 70, preferably between 35 and 65, preferably 40 and 60, very preferably between 45 and 55. Without being bound to any theory, it has been discovered that, to minimize the thermal load of the raffinate column, this spacing is correlated with the quality of the prefractionation of the raffinates carried out in step A. Preferably in order to minimize the thermal load of the column B-C2 when the quality of the pre-fractionation varies, the injection of fraction A22 will be done by a distribution system on different trays so that the spacing between the injection points of the charges A21 and A22 increases when the parameter separation R increases. Said 2-section column further comprises a condenser and a reboiler, operated at 0.2 MPa with a reflux rate of 1.2.
Dans un mode de réalisation particulier, lorsque le désorbant mis en œuvre à l’étape A est un composé plus lourd que les xylènes, c’est-à-dire présentant un point d’ébullition plus élevé que celui des xylènes, le raffinât enrichi en désorbant, c’est à dire la fraction A22, est introduit en dessous du raffinât appauvri en désorbant, c’est à dire la fraction A21. In a particular embodiment, when the desorbent used in step A is a heavier compound than the xylenes, that is to say having a higher boiling point than that of the xylenes, the enriched raffinate by desorbing, ie the fraction A22, is introduced below the depleted raffinate by desorbing, ie the fraction A21.
Dans un autre mode de réalisation, lorsque le désorbant de ladite étape de séparation est un composé plus léger que les xylènes, c’est-à-dire présentant un point d’ébullition plus faible que celui des xylènes, le raffinât enrichi en désorbant, c’est à dire la fraction A21, est introduit au-dessus du raffinât appauvri en désorbant, c’est à dire la fraction A22. In another embodiment, when the desorbent of said separation step is a lighter compound than the xylenes, that is to say having a lower boiling point than that of the xylenes, the raffinate enriched in desorbent, that is to say the fraction A21, is introduced above the depleted raffinate by desorbing, that is to say the fraction A22.
Dans un autre mode de réalisation, la colonne de distillation mise en œuvre est une colonne 3 coupes. De préférence, ladite colonne comprend une paroi interne placée, de préférence, dans la zone de rectification et permet de recueillir deux fractions B2 et B3 exemptes de désorbant et une fraction B42 exempte de C8A et comprenant, de préférence constitué, de désorbant. In another embodiment, the distillation column used is a 3-section column. Preferably, said column comprises an internal wall preferably placed in the rectification zone and makes it possible to collect two fractions B2 and B3 free of desorbent and a fraction B42 free of C8A and comprising, preferably consisting of desorbent.
De préférence, l’injection des fractions A21 et A22 est réalisée de part et d’autre de la paroi interne. En d’autres termes, avantageusement, les positions des deux alimentations des fractions A21 et A22 se situent de part et d’autre de la paroi interne. Preferably, the injection of the fractions A21 and A22 is carried out on either side of the internal wall. In other words, advantageously, the positions of the two supplies of the fractions A21 and A22 are located on either side of the internal wall.
De préférence, la fraction Al issue de l’étape A contenant, et de préférence constituée, d’un mélange de PX et de désorbant est engagée dans une étape de fractionnement par distillation dans une colonne de distillation (B-Cl) permettant l’obtention d’une fraction B1 exempte de désorbant constituée de PX et une fraction B41 constituée de désorbant. Ladite distillation est mise en œuvre selon les connaissances de l’Homme du métier. Preferably, the fraction Al originating from stage A containing, and preferably consisting of, a mixture of PX and desorbent is engaged in a fractionation stage by distillation in a distillation column (B-Cl) allowing the obtaining a fraction B1 free of desorbent consisting of PX and a fraction B41 consisting of desorbent. Said distillation is carried out according to the knowledge of a person skilled in the art.
Avantageusement, les fractions désorbant B41 et B42 exemptes de C8A sont récupérées en fond de chaque colonne de distillation, lorsque le désorbant est lourd et en tête lorsque le désorbant est léger. Lesdites fractions sont ensuite mélangées et renvoyées vers l’étape A d’adsorption en lit mobile simulé par l’intermédiaire du flux B4. Etape C d’isomérisation en phase vapeur Advantageously, the desorbent fractions B41 and B42 free of C8A are recovered at the bottom of each distillation column, when the desorbent is heavy and at the head when the desorbent is light. Said fractions are then mixed and returned to step A of adsorption in a simulated moving bed by means of stream B4. Steam phase isomerization step C
Le procédé comprend en outre une étape C d’isomérisation en phase vapeur de la fraction B2 comprenant de l’éthylbenzène, de l’orthoxylène et du métaxylène issu de l’étape B de fractionnement. The process further comprises a step C of isomerization in the vapor phase of the fraction B2 comprising ethylbenzene, orthoxylene and metaxylene from step B of fractionation.
Avantageusement l’étape C d’isomérisation en phase vapeur permet l’isomérisation des xylènes ainsi que de 1ΈB, dans une unité opérant en phase vapeur, à haute température et convertissant l’éthylbenzène en xylènes, pour traiter le raffinât B2 riche en EB issu de l’étape B. Advantageously, step C of isomerization in the vapor phase allows the isomerization of the xylenes as well as of 1ΈB, in a unit operating in the vapor phase, at high temperature and converting ethylbenzene into xylenes, to treat the raffinate B2 rich in EB from from step B.
L’étape d’isomérisation en phase vapeur permet de convertir 1ΈB en xylènes avec un taux de conversion par passe de l’éthylbenzène généralement comprise entre 10 et 50%, de préférence comprise entre 20 et 40%, avec une perte en C8 Aromatiques (C8A) inférieure à 5,0 %poids, de préférence inférieure à 3,0 % poids et préférentiellement inférieure à 1,8 % poids. The vapor phase isomerization stage makes it possible to convert 1ΈB into xylenes with a pass conversion rate of ethylbenzene generally between 10 and 50%, preferably between 20 and 40%, with a loss of C8 Aromatics ( C8A) less than 5.0% by weight, preferably less than 3.0% by weight and preferably less than 1.8% by weight.
Avantageusement ladite étape C permet également d’isomériser les xylènes, de telle sorte que le paraxylène (PX) ait une concentration à l’équilibre thermodynamique; définie par Advantageously, said step C also makes it possible to isomerize the xylenes, so that the paraxylene (PX) has a concentration at thermodynamic equilibrium; defined by
(Ceff-Cin)xlOO /(Ceq -Cin)  (Ceff-Cin) xlOO / (Ceq -Cin)
dans lesquels wherein
Ceff et Cin sont les concentrations en PX respectivement dans la coupe C8A de l’effluent et de la charge du réacteur d’isomérisation,  Ceff and Cin are the PX concentrations respectively in section C8A of the effluent and of the charge of the isomerization reactor,
Ceq est la concentration à l’équilibre thermodynamique du PX dans la coupe C8A à la température réactionnelle ; supérieure ou égale à 90%.  Ceq is the thermodynamic equilibrium concentration of PX in section C8A at reaction temperature; greater than or equal to 90%.
L’étape d’isomérisation en phase vapeur est mise en œuvre à une température supérieure à 300°C, de préférence comprise entre 350 et 480°C, une pression inférieure à 4,0 MPa, de préférence comprise entre 0,5 et 2,0 MPa, une vitesse spatiale inférieure à 10,0 h 1, de préférence comprise entre 0,5 et 6,0 h 1, rapport molaire hydrogène sur hydrocarbure inférieur à 10,0, de préférence compris entre 3,0 et 6,0, et en présence d’un catalyseur comportant au moins une zéolithe présentant des canaux dont l’ouverture est définie par un anneau à 10 ou 12 atomes d’oxygène (10 MR ou 12 MR), et au moins un métal du groupe VIII de teneur comprise entre 0,1 et 0,3% poids. The vapor phase isomerization step is carried out at a temperature above 300 ° C, preferably between 350 and 480 ° C, a pressure below 4.0 MPa, preferably between 0.5 and 2 0.0 MPa, a space velocity less than 10.0 h 1 , preferably between 0.5 and 6.0 h 1 , hydrogen to hydrocarbon molar ratio less than 10.0, preferably between 3.0 and 6, 0, and in the presence of a catalyst comprising at least one zeolite having channels whose opening is defined by a ring with 10 or 12 oxygen atoms (10 MR or 12 MR), and at least one metal from group VIII of content between 0.1 and 0.3% by weight.
Tous les catalyseurs susceptibles d’isomériser les hydrocarbures à 8 atomes de carbone, zéolitiques ou non, conviennent pour l’unité d’isomérisation en phase vapeur. De préférence, on utilise un catalyseur contenant une zéolithe acide, par exemple de type structural MFI, MOR, MAZ, FAU et/ou EUO. De manière encore plus préférée, on utilise un catalyseur contenant une zéolithe de type structural EUO et au moins un métal du groupe VIII de la classification périodique des éléments. Selon une variante préférée du procédé, le catalyseur utilisé à l’étape C comprend de 1 à 70% poids d’une zéolithe de type structural Lt 10, de préférence LU- 1 , comprenant du silicium et au moins un élément T choisi de préférence parmi l’aluminium et le bore dont le rapport Si/T est compris entre 5 et 100. De préférence, la zéolithe est sous forme hydrogène au moins en partie, et la teneur en sodium est telle que le ratio atomique Na/T est inférieur à 0,1. All the catalysts capable of isomerizing hydrocarbons with 8 carbon atoms, zeolitic or not, are suitable for the vapor phase isomerization unit. Preferably, a catalyst is used containing an acidic zeolite, for example of the structural type MFI, MOR, MAZ, FAU and / or EUO. Even more preferably, a catalyst is used containing a zeolite of structural type EUO and at least one metal from group VIII of the periodic table. According to a preferred variant of the process, the catalyst used in step C comprises from 1 to 70% by weight of a zeolite of structural type Lt 10, preferably LU-1, comprising silicon and at least one element T preferably chosen among aluminum and boron whose Si / T ratio is between 5 and 100. Preferably, the zeolite is in hydrogen form at least in part, and the sodium content is such that the atomic ratio Na / T is lower at 0.1.
De préférence, le catalyseur comprend entre 0,01 et 2% poids d’étain ou d’indium, et du soufre à raison de 0,5 à 2 atomes par atome de métal du groupe VIII. Preferably, the catalyst comprises between 0.01 and 2% by weight of tin or indium, and sulfur in an amount of 0.5 to 2 atoms per atom of group VIII metal.
L’effluent Cl obtenu à l’étape C, présentant des concentrations en isomère PX, OX et MX proches des concentrations de l’équilibre thermodynamique sont recyclés vers l’étape A d’adsorption en ht mobile simulé. The Cl effluent obtained in step C, having concentrations of the PX, OX and MX isomer close to the thermodynamic equilibrium concentrations, are recycled to step A of adsorption in simulated mobile ht.
Dans un mode de réalisation particulier, lorsque l’effluent Cl contient des composés lourds et légers formés par les réactions indésirables ledit effluent est alors engagé dans une étape optionnelle de fractionnement pour éliminer lesdits composés. EXEMPLES In a particular embodiment, when the effluent Cl contains heavy and light compounds formed by the undesirable reactions, said effluent is then engaged in an optional fractionation step to remove said compounds. EXAMPLES
Les exemples ci-dessous illustrent l’invention sans en limiter la portée. The examples below illustrate the invention without limiting its scope.
Exemple 1 : Example 1:
Cet exemple montre l’intérêt de l’invention en comparant les performances de l’étape de distillation B placée entre une étape d’adsorption A et une étape d’isomérisation C, lesdites étapes faisant partie d’un complexe aromatique produisant du paraxylène à partir d’un reformat. This example shows the advantage of the invention by comparing the performance of the distillation step B placed between an adsorption step A and an isomerization step C, said steps being part of an aromatic complex producing paraxylene at from a reformat.
Dans cet exemple on considère 543 t/h d’une coupe C8 issue d’une colonne de xylène et comprenant des C8Aromatiques (C8A) provenant d’un réformat, d’une unité de transalkylation et d’une ou plusieurs unités d’isomérisation, sa composition est en % poids : In this example we consider 543 t / h of a C8 cut coming from a xylene column and comprising C8Aromatics (C8A) coming from a reformate, from a transalkylation unit and from one or more isomerization units , its composition is in% by weight:
Figure imgf000013_0001
Selon l’état de l’art représenté sur la figure lb), cette coupe C8A est envoyée dans une étape A d’adsorption en lit mobile simulé comprenant un adsorbeur avec 4 zones délimitées par les injections de charges et de désorbant B4 et les soutirages de raffmat A2 et d’extrait Al. Cet adsorbeur est composé de 15 lits contenant de la zéolithe X échangée au baryum répartis comme suit :
Figure imgf000013_0001
According to the state of the art represented in FIG. 1b), this section C8A is sent in a step A of adsorption in a simulated moving bed comprising an adsorber with 4 zones delimited by the injections of charges and desorbent B4 and the withdrawals of Raffmat A2 and of extract Al. This adsorber is composed of 15 beds containing X zeolite exchanged with barium distributed as follows:
o 3 lit en Zone 1, comprise entre l’injection du désorbant B4 et le soutirage de l’extrait Al. o 6 lits en zone 2 , comprise entre le soutirage de l’extrait Al et l’injection de la charge o 4 lits en zone 3, comprise entre l’injection de la charge et le soutirage du raffmat A2 o 2 lits en zone 4, comprise entre le soutirage du raffinât A2 et l’injection du désorbant B4  o 3 beds in Zone 1, between the injection of the desorbent B4 and the withdrawal of the extract Al o 6 beds in zone 2, between the withdrawal of the extract Al and the injection of the load o 4 beds in zone 3, between the injection of the charge and the withdrawal of the raffmat A2 or 2 beds in zone 4, between the withdrawal of the raffinate A2 and the injection of the desorbent B4
La température est de 175 °C. Le désorbant utilisé est le Paradiéthylbenzène, le taux de solvant par rapport à la charge est de 1,2 (vol/vol). The temperature is 175 ° C. The desorbent used is Paradiethylbenzene, the level of solvent relative to the charge is 1.2 (vol / vol).
Ainsi mise en œuvre l’unité de séparation par adsorption A permet de produire 2 flux Al et A2 alimentant l’étape de distillation B : Thus, the adsorption separation unit A is used to produce 2 streams Al and A2 supplying the distillation step B:
*Un extrait Al contenant au moins 97 % du PX de la charge et une partie du désorbant, lequel est envoyé dans une colonne d’extrait B-Cl afin de récupérer le PX pur en tête (flux Bl) et l’adsorbant en fond (flux B41). * An Al extract containing at least 97% of the PX of the feed and part of the desorbent, which is sent to a column of B-Cl extract in order to recover the pure PX at the head (flow Bl) and the adsorbent at the bottom (flow B41).
*827,9 t/h d’un raffmat A2 substantiellement exempt de PX, contenant 407,1 t/h de désorbant le raffmat A2 est alimenté au plateau théorique 25 dans la colonne de distillation B-C2 contenant 47 plateaux théoriques, un condenseur et un rebouilleur, opérée à 0,2 MPa avec un taux de reflux de 1 ,4- Cette colonne permet de produire 2 flux : 420 t/h d’un raffmat en tête B2 contenant 25 ppm de désorbant et de 407 t/h de désorbant B42 en fond contenant 50ppm de xylènes et renvoyé au lit mobile simulé, après mélange avec le flux B41, et échange thermique à la température requise pour G adsorption. Le fractionnement du raffmat A2 par la colonne de raffmat décrit ainsi nécessite 80 Gcal/h d’énergie de rebouillage. Le raffmat B2 est envoyé vers la première étape d’isomérisation (C). * 827.9 t / h of a raffmat A2 substantially free of PX, containing 407.1 t / h of desorbent, the raffmat A2 is fed to the theoretical plate 25 in the distillation column B-C2 containing 47 theoretical plates, a condenser and a reboiler, operated at 0.2 MPa with a reflux rate of 1.4, This column makes it possible to produce 2 flows: 420 t / h of a raffmat at the head B2 containing 25 ppm of desorbent and of 407 t / h of desorbent B42 at the bottom containing 50 ppm of xylenes and returned to the simulated moving bed, after mixing with the flow B41, and heat exchange at the temperature required for G adsorption. The fractionation of the raffmat A2 by the raffmat column described thus requires 80 Gcal / h of reboiling energy. Raffmat B2 is sent to the first isomerization step (C).
Dans une mise en œuvre du procédé selon l’invention représenté sur la figure 2), ladite coupe C8A est envoyée dans une étape A d’adsorption en lit mobile simulé comprenant un adsorbeur avec 5 zones délimitées par les injections de charges et de désorbant (B4) et les soutirages des raffmats A21, A22 et d’extrait Al. Ledit adsorbeur est composé de 18 lits contenant de la zéolithe X échangée au baryum répartis comme suit : In an implementation of the method according to the invention shown in FIG. 2), said section C8A is sent in a step A of adsorption in a simulated moving bed comprising an adsorber with 5 zones delimited by the injections of fillers and desorbent ( B4) and the withdrawals of the raffmates A21, A22 and of extract Al. Said adsorber is composed of 18 beds containing zeolite X exchanged with barium distributed as follows:
o 3 lit en Zone 1, comprise entre l’injection du désorbant B4 et le soutirage de l’extrait Al, o 6 lits en zone 2 , comprise entre le soutirage de l’extrait Al et l’injection de la charge, o 4 lits en zone 3A, comprise entre l’injection de la charge et le soutirage du raffrnat A21, o 3 lits en zone 3B, comprise entre le soutirage du raffrnat A21 et le soutirage du raffinât A22, o 2 lits en zone 4, comprise entre le soutirage du raffinât A22 et l’injection du désorbant B4. o 3 beds in Zone 1, between the injection of the desorbent B4 and the withdrawal of the extract Al, o 6 beds in zone 2, between the withdrawal of the extract Al and the injection of the load, o 4 beds in zone 3A, between the injection of the load and the withdrawal of the A21 raffrnate, o 3 beds in zone 3B, between the withdrawal of raffinate A21 and the withdrawal of raffinate A22, o 2 beds in zone 4, between the withdrawal of raffinate A22 and the injection of desorbent B4.
La température est de 175 °C. Le désorbant utilisé est le Paradiéthylbenzène, le taux de solvant par rapport à la charge est de 1,2 (vol/vol). The temperature is 175 ° C. The desorbent used is Paradiethylbenzene, the level of solvent relative to the charge is 1.2 (vol / vol).
Ainsi la mise en œuvre à l’étape A de l’unité de séparation par adsorption selon l’invention permet d’obtenir trois fractions Al, A21, et A22, selon la répartition suivante. Thus the implementation in step A of the adsorption separation unit according to the invention makes it possible to obtain three fractions Al, A21, and A22, according to the following distribution.
- Lin extrait Al contenant au moins 97 % du paraxylène PX de la charge et une partie du désorbant, lequel est envoyé dans une colonne d’extrait afin de récupérer le PX pur en tête et le désorbant en fond.  - Lin extract Al containing at least 97% of the paraxylene PX of the feed and part of the desorbent, which is sent to an extract column in order to recover the pure PX at the top and the desorbent at the bottom.
- 507,5t/h de raffinât léger A21 et  - 507.5t / h of light raffinate A21 and
- 320,4 t/h de raffinât lourd A22.  - 320.4 t / h of heavy raffinate A22.
Les raffinats A21 et A22 sont soutirés de part et d’autre de la zone 3B de l’unité A d’ adsorption en lit mobile simulé, et présentent les compositions suivantes : The raffinates A21 and A22 are drawn off on either side of zone 3B of the unit A of adsorption in simulated moving bed, and have the following compositions:
• R(C8A), la quantités de C8A dans le raffinât A21 / la quantité de C8A dans le raffinât total = 79%  • R (C8A), the quantity of C8A in the raffinate A21 / the quantity of C8A in the total raffinate = 79%
• R(Désorbant), la quantité de désorbant dans le raffinât A21/ la quantité de désorbant dans le raffinât total = 43%  • R (Desorbent), the amount of desorbent in the raffinate A21 / the amount of desorbent in the total raffinate = 43%
• Le paramètre de séparation Delta R = 36%  • Delta R separation parameter = 36%
Lors de l’étape B de fractionnement par la colonne de distillation B-C2 contenant 47 plateaux théoriques, le raffinât A21 est alimenté au plateau théorique 24, et le raffinât A22 est alimenté au plateau théorique 30. Ladite colonne comprend en outre un condenseur et un rebouilleur, opérée à 0,2 MPa avec un taux de reflux de 1 ,2. Ladite colonne permet de produire les 2 fractions suivantes : During step B of fractionation by the distillation column B-C2 containing 47 theoretical plates, the raffinate A21 is fed to the theoretical plate 24, and the raffinate A22 is fed to the theoretical plate 30. Said column further comprises a condenser and a reboiler, operated at 0.2 MPa with a reflux rate of 1.2. Said column makes it possible to produce the following 2 fractions:
- 420 t/h d’un raffinât en tête B2 contenant du MX, OX, EB et 25 ppm de désorbant et  - 420 t / h of a raffinate at the top B2 containing MX, OX, EB and 25 ppm of desorbent and
- de 407 t/h de désorbant B42 en fond contenant 50ppm de xylènes et renvoyé au lit mobile simulé, après mélange avec le flux B41, et échange thermique à la température requise pour l’ adsorption. Le fractionnement des raffinats A21 et A22 par la colonne de raffinât décrit ainsi nécessite 74,4 Gcal/h d’énergie de rebouillage. Le raffrnat B2 est envoyé vers l’étape C d’isomérisation. Cet exemple illustre clairement que l’obtention d’un raffinât enrichi en désorbant et d’un raffinât enrichi en MX, OX, EB par la mise en œuvre dans une étape A de séparation d’une unité d’adsorption en lit mobile simulé, associée à leur introduction séparée dans une colonne de distillation permet de faciliter leur fractionnement et ainsi d’alléger sa charge thermique. Contrairement au procédé décrit dans l’état de l’art où la colonne de raffinât n’est alimentée que par une charge, il est, conformément au procédé selon l’invention, possible de réduire la charge thermique du rebouilleur de 7%, sans ajouter d’autre étapes ou autre équipement au complexe aromatique connu dans l’état de l’art. - 407 t / h of desorbent B42 at the bottom containing 50 ppm of xylenes and returned to the simulated moving bed, after mixing with the flow B41, and heat exchange at the temperature required for adsorption. The fractionation of the raffinates A21 and A22 by the raffinate column described thus requires 74.4 Gcal / h of reboiling energy. The B2 raffrnate is sent to step C of isomerization. This example clearly illustrates that obtaining a raffinate enriched in desorbent and a raffinate enriched in MX, OX, EB by the implementation in a step A of separation of an adsorption unit in simulated moving bed, associated with their separate introduction into a distillation column makes it possible to facilitate their fractionation and thus to reduce its thermal load. Unlike the process described in the state of the art where the raffinate column is only supplied with a charge, it is, in accordance with the process according to the invention, possible to reduce the thermal load of the reboiler by 7%, without add other steps or other equipment to the aromatic complex known in the state of the art.
Exemple 2 : Cet exemple illustre l’intérêt de l’invention, lorsque les performances du préfractionnement du raffinât lors de l’étape A d’adsorption varient, comme cela peut arriver par exemple au cours d’un changement de réglage des paramètres opératoires de l’adsorbeur ou d’un changement de tamis moléculaire. Les conditions de cet exemple sont identiques à celles de l’exemple 1. on simule une variation du paramètre de séparation obtenu via un changement de tamis. La position de l’alimentation du raffinât léger A21 dans la colonne de raffinât n’est pas impactée, celle du raffinât lourd est très légèrement modifiée, le gain de charge thermique du rebouilleur augmente significativement avec la qualité du préfractionnement du raffinât. Example 2: This example illustrates the advantage of the invention, when the performances of the prefractionation of the raffinate during the adsorption stage A vary, as can happen for example during a change of setting of the operating parameters of the adsorber or a change of molecular sieve. The conditions of this example are identical to those of Example 1. we simulate a variation of the separation parameter obtained via a change of sieve. The position of the feed of the light raffinate A21 in the raffinate column is not impacted, that of the heavy raffinate is very slightly modified, the gain in thermal load of the reboiler increases significantly with the quality of the pre-fractionation of the raffinate.
L’amélioration des capacités et des sélectivités d’adsorption du tamis moléculaire peuvent être mises à profit pour réduire la consommation énergétique du complexe aromatique sans modification de la configuration du complexe aromatique ni de ses performances en terme de productivité. The improvement of the adsorption capacities and selectivities of the molecular sieve can be used to reduce the energy consumption of the aromatic complex without modifying the configuration of the aromatic complex nor its performance in terms of productivity.
état de l’art casl cas 2 cas 3 state of the art casl case 2 case 3
R(C8A) ï 0/78 0,78 0,88R (C8A) ï 0/78 0.78 0.88
R(Désorbant), 1 0,43 0,33 0,33R (Desorbent), 1 0.43 0.33 0.33
Paramètre de séparation Delta R 0 0,36 0,45 0,55Separation parameter Delta R 0 0.36 0.45 0.55
Position de G alimentation A2 25 NA NA NAPosition of G supply A2 25 NA NA NA
Position de G alimentation A22 NA 29 30 31Position of G supply A22 NA 29 30 31
Position de l’alimentation A21 NA 24 24 24Supply position A21 NA 24 24 24
Charge thermique du rebouilleur (Gcal/h) 80,0 74,4 72,6 71,0Reboiler thermal load (Gcal / h) 80.0 74.4 72.6 71.0
Gain énergétique 7% 9% 11% Energy gain 7% 9% 11%

Claims

REVENDICATIONS
1. Un procédé d’obtention de paraxylène à partir d’une charge contenant des xylènes, de l’éthylbenzène et des hydrocarbures en C9+, ledit procédé comprenant 1. A process for obtaining paraxylene from a feed containing xylenes, ethylbenzene and C9 + hydrocarbons, said process comprising
- une unique étape A de séparation en lit mobile simulé de ladite charge, ladite étape étant mise en œuvre avec une zéolithe comme adsorbant et un désorbant, à une température comprise entre 20 et 250°C, sous une pression comprise entre la pression de bulle des xylènes à la température opératoire et 2,0 MPa, et avec un rapport volumique du désorbant sur la charge dans l’unité de séparation en lit mobile simulé est compris entre 0,4 et 2,5, et permettant l’obtention d’au moins trois fractions,  a single step A of separation in a simulated moving bed of said charge, said step being carried out with a zeolite as adsorbent and a desorbent, at a temperature between 20 and 250 ° C., under a pressure comprised between the bubble pressure xylenes at operating temperature and 2.0 MPa, and with a volume ratio of the desorbent to the charge in the separation unit in simulated moving bed is between 0.4 and 2.5, and allowing obtaining at least three fractions,
■ une fraction Al comprenant un mélange de paraxylène et de désorbant, et ■ an Al fraction comprising a mixture of paraxylene and desorbent, and
■ deux fractions A21, A22 comprenant de l’éthylbenzène (EB), de l’orthoxylène (OX) et du métaxylène (MX) et du désorbant, ■ two fractions A21, A22 comprising ethylbenzene (EB), orthoxylene (OX), and metaxylene (MX) and desorbent,
- une étape B de fractionnement par distillation dans une colonne de distillation des fractions A21 et A22 issue de l’étape A, dans laquelle lesdites fractions sont introduites séparément à des points d’injections distincts et permet l’obtention d’une fraction B2 contenant de l’éthylbenzène, de l’orthoxylène et du métaxylène, et une fraction B42 exempte de composés aromatique contenant 8 atomes de carbones et contenant du désorbant.  a stage B of fractionation by distillation in a distillation column of the fractions A21 and A22 resulting from stage A, in which the said fractions are introduced separately at separate injection points and makes it possible to obtain a fraction B2 containing ethylbenzene, orthoxylene and metaxylene, and a fraction B42 free of aromatic compounds containing 8 carbon atoms and containing desorbent.
2. Procédé selon la revendication 1 dans lequel la colonne de distillation mise en œuvre à l’étape B présente un nombre de plateaux théoriques compris entre 30 et 80, de préférence entre 35 et 75, de manière préférée 40 et 70, de manière très préférée entre 45 et 65. 2. Method according to claim 1 wherein the distillation column used in step B has a number of theoretical plates of between 30 and 80, preferably between 35 and 75, preferably 40 and 70, very preferred between 45 and 65.
3. Procédé selon l’une quelconque des revendications précédentes dans lequel les points injections des fractions A21 et A22 dans la colonne de distillation mise en œuvre à l’étape B présente un écartement compris entre 2 et 15 plateaux théoriques, de préférence entre 3 et 12. 3. Method according to any one of the preceding claims, in which the injection points of the fractions A21 and A22 in the distillation column implemented in step B have a spacing of between 2 and 15 theoretical plates, preferably between 3 and 12.
4. Procédé selon l’une quelconque des revendications 1 à 3 dans lequel la colonne de distillation mise en œuvre à l’étape B est choisie parmi une colonne 2 coupes et une colonne 3 coupes. 4. Method according to any one of claims 1 to 3 wherein the distillation column used in step B is chosen from a 2-section column and a 3-section column.
5. Procédé selon l’une quelconque des revendications précédentes dans lequel la fraction A21 présente une teneur massique en désorbant inférieure à celle de la fraction A22. 5. Method according to any one of the preceding claims, in which the fraction A21 has a mass content of desorbent less than that of the fraction A22.
6. Procédé selon l’une quelconque des revendications précédentes dans lequel l’étape A de séparation en lit mobile simulé est mise en œuvre à une température comprise 90 et 2lO°C, et sous une pression comprise entre 1 ,0 et 2,2 MPa. 6. Method according to any one of the preceding claims, in which step A of separation in a simulated moving bed is carried out at a temperature of between 90 and 21 ° C., and under a pressure of between 1.0 and 2.2. MPa.
7. Procédé selon l’une quelconque des revendications précédentes dans lequel le nombre total de lits de l’unité de séparation (SMB) mis en œuvre à l’étape A est compris entre 10 et 30 lits, et de manière préférée, entre 15 et 18 lits. 7. Method according to any one of the preceding claims, in which the total number of beds of the separation unit (SMB) implemented in step A is between 10 and 30 beds, and preferably between 15 and 18 beds.
8. Procédé selon l’une quelconque des revendications 5 à 7 dans lequel le désorbant mis en œuvre à l’étape A est un composé présentant un point d’ébullition plus élevé que celui des xylènes, et la fraction A22 est introduite en dessous de la fraction A21. 8. Method according to any one of claims 5 to 7 wherein the desorbent used in step A is a compound having a higher boiling point than that of xylenes, and the fraction A22 is introduced below fraction A21.
9. Procédé selon l’une quelconque des revendications 5 à 7 dans lequel le désorbant mis en œuvre à l’étape A est un composé présentant un point d’ébullition plus faible que celles des xylènes, et la fraction A22 est introduite au-dessus de la A21. 9. Method according to any one of claims 5 to 7 wherein the desorbent used in step A is a compound having a lower boiling point than those of xylenes, and the fraction A22 is introduced above from the A21.
10. Procédé selon l’une quelconque des revendications précédentes comprenant une étape C d’isomérisation en phase vapeur de la fraction B2 comprenant de l’éthylbenzène, de l’orthoxylène et du métaxylène issu de l’étape B de fractionnement. 10. Method according to any one of the preceding claims comprising a step C of isomerization in the vapor phase of the fraction B2 comprising ethylbenzene, orthoxylene and metaxylene resulting from step B of fractionation.
11. Procédé selon la revendication 10 dans lequel l’étape d’isomérisation est mise en œuvre à une température supérieure à 300°C, de préférence comprise entre 350 et 480°C, une pression inférieure à 4,0 MPa, de préférence comprise entre 0,5 et 2,0 MPa, une vitesse spatiale inférieure à 10,0 h-l, de préférence comprise entre 0,5 et 6,0 h 1, rapport molaire hydrogène sur hydrocarbure inférieur à 10,0, de préférence compris entre 3,0 et 6,0, et en présence d’un catalyseur comportant au moins une zéolithe présentant des canaux dont l’ouverture est définie par un anneau à 10 ou 12 atomes d’oxygène (10 MR ou 12 MR), et au moins un métal du groupe VIII de teneur comprise entre 0,1 et 0,3% poids. 11. The method of claim 10 wherein the isomerization step is carried out at a temperature above 300 ° C, preferably between 350 and 480 ° C, a pressure below 4.0 MPa, preferably between between 0.5 and 2.0 MPa, a space velocity of less than 10.0 hl, preferably of between 0.5 and 6.0 h 1 , hydrogen to hydrocarbon molar ratio of less than 10.0, preferably of between 3 , 0 and 6.0, and in the presence of a catalyst comprising at least one zeolite having channels whose opening is defined by a ring with 10 or 12 oxygen atoms (10 MR or 12 MR), and at least a group VIII metal with a content of between 0.1 and 0.3% by weight.
PCT/EP2019/066445 2018-06-29 2019-06-21 Method for producing paraxylene using a simulated moving-bed step, and a step of fractionating two fractions in a two-section column WO2020002142A1 (en)

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KR1020207036182A KR20210030273A (en) 2018-06-29 2019-06-21 Method for producing paraxylene using a pseudo-moving bed step, and fractionating two fractions in a two-section column
US17/256,290 US11242302B2 (en) 2018-06-29 2019-06-21 Method for producing paraxylene using a simulated moving-bed step, and a step of fractionating two fractions in a two-section column
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